Oil pump driving structure of automatic transmission

ABSTRACT

There is provided an oil pump driving structure of an automatic transmission which can prevent slack of a chain, which is looped over a drive sprocket on a main shaft and a driven sprocket of an oil pump, and resulting poor engagement of the chain and the driven sprocket by a simple construction. A chain guide is projected integrally from an end face of a housing cover attached to an opening of a switching unit housing in a transmission case and is located in the vicinity of the driven sprocket. The chain guide guides a slacked side of the chain through a path closer to a tensioned side of the chain. As a result, even if the accuracy of the center distance between a drive sprocket and the driven sprocket is not improved, vibration of the chain can be suppressed to improve quietness.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oil pump driving structure in an automatic transmission of a vehicle, in which an oil pump is disposed apart from a main shaft and driven by driving force transmitted from the main shaft via a chain.

2. Discription of the Prior Art

Conventionally, as an oil pump that supplies lubricating oil and operating oil to component parts of an automatic transmission, there has been known an oil pump that is disposed apart from a main shaft connected to a torque converter and is driven via a chain looped over a drive sprocket, which is rotated on a main shaft by driving force from an engine, and a driven sprocket of the oil pump.

In a mounting structure of such an oil pump, the drive sprocket is located on the main shaft supported by a transmission case and between a forward/backward switching unit and the torque converter, and is engaged with a hollow shaft extending from a converter case that supports therein an impeller of the torque converter.

On the other hand, an oil pump mounting surface of the transmission case is set at a location retracted from the drive sprocket in the axial direction by the length of the oil pump so that the driven sprocket provided at a front end of the oil pump with a back surface thereof abutted and fixed on the oil pump mounting surface can be aligned with the drive sprocket in the axial direction. As a result, driving force is transmitted without causing the chain looped over the drive sprocket and the driven sprocket to fall off.

Here, the accuracy of the center distance between the rotary shaft of the driven sprocket of the oil pump and the main shaft that supports the drive sprocket is important in ensuring quietness.

However, the oil pump mounting surface is apart from the main shaft and offset from the drive sprocket to a considerable degree in the axial direction although the oil pump mounting surface is formed on the transmission case that supports the main shaft on which the drive sprocket is located. Thus, a margin of error in the center distance between the rotary shaft of the driven sprocket of the oil pump fixed to the oil pump mounting surface and the main shaft that supports the drive sprocket is inevitably large.

Moreover, since the oil pump is supported only in the back side thereof like a cantilever, the margin of error tends to be increased due to tension of the chain when the oil pump is driven, making it difficult to ensure quietness.

To address this problem, a method in which the drive sprocket and the driven sprocket are supported in the same case such as a converter housing opposed to the transmission case so as to improve the accuracy of the center distance between the drive sprocket and the driven sprocket has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-301929, for example.

In the above method proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2003-301929, after the drive sprocket and the driven sprocket are fitted on a support on the converter housing, the driven sprocket must be engaged with the shaft of the oil pump mounted on the transmission case at the same time when the converter housing is attached to the transmission case. To this end, the oil pump mounted on the transmission case is required to have high positional accuracy, but no arrangement therefore is mentioned. Thus, the problem that the chain slacks excessively and resulting poor engagement of the chain and the driven sprocket is still unsolved.

Also, a holding mechanism is required so as to prevent the drive sprocket and the driven sprocket from falling off the converter housing before the converter housing is attached to the transmission case, and therefore structure is complicated.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an oil pump driving structure of an automatic transmission which can prevent slack of a chain and resulting poor engagement of the chain and a driven sprocket by a simple construction.

To attain the above object, there is provided an oil pump driving structure of an automatic transmission, including an oil pump disposed apart from a main shaft of the automatic transmission, a chain looped over a drive sprocket provided on the main shaft and a driven sprocket of the oil pump, for transmitting revolutions from the drive sprocket to the driven sprocket, and a chain guide that guides a slacked side of the chain through a path that reduces the amount of the slack.

According to the present invention, the chain guide guides the slacked side of the chain through the path that can reduce the amount of the slack. As a result, even if the accuracy of the center distance between the drive sprocket and the driven sprocket is not improved, vibration of the chain can be suppressed enough to improve quietness, and poor engagement of the chain and the driven sprocket can be prevented.

Other features and advantages of the present invention will apparent from the following detailed description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially longitudinal sectional view showing an automatic transmission according to an embodiment of the present invention;

FIG. 2 is a front view showing an area where a chain is looped; and

FIG. 3 is a sectional view taken along line A-A in FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described in detail with reference to the drawings showing a preferred embodiment thereof.

FIG. 1 is a partially longitudinal sectional view showing an automatic transmission according to an embodiment of the present invention. FIG. 2 is a front view showing an area where a chain is looped.

As shown in FIG. 1, a main shaft 13 is disposed in a manner extending between a converter housing 11 and a transmission case 12. Along the main shaft 13, a torque converter 15 is housed in the converter housing 11, and a switching unit housing 30 housing a forward/backward switching unit 31 is formed in the transmission case 12 in a manner being opposed to the converter housing 11.

A converter case 16 that supports an impeller 17 of the torque converter 15 has a front end thereof connected to a crankshaft of an engine, not shown, and a rear end thereof provided with a hollow shaft 20 extending toward the transmission case 12.

A housing cover 40 is attached to an opening of the switching unit housing 30 and includes a hollow cylindrical shaft-supporting cylinder 45 pressed into a base 41 in the central part of the housing cover 40. The shaft supporting cylinder 45 supports the main shaft 13 penetrated therein, and the outer periphery of the shaft supporting cylinder 45 supports the hollow shaft 20 extending from the converter case 16. Further, the shaft supporting cylinder 45 extends into the torque converter 15 and has a front end thereof splined to a stator supporting part 18.

A drive sprocket 47 is disposed adjacent to the base 41 of the housing cover 40 and on the converter housing 11 side of the base 41. The drive sprocket 47 has the inner periphery thereof supported by and splined to an end of the hollow shaft 20 so that the drive sprocket 47 can rotate integrally with the converter case 16.

As shown in FIG. 2, in the lower part of the transmission case 12, an oil pump 50 is disposed adjacent to the switching unit housing 30. An oil pan, not shown, is mounted on a lower end face of the transmission case 12 where the oil pump 50 is disposed.

As shown in FIG. 1, the transmission case 12 is comprised of an oil pump mounting surface 33 offset rearward from the opening of the switching unit housing 30 to which the housing cover 40 is attached, and the oil pump 50 is fastened on the oil pump mounting surface 33 by a bolt 35.

It should be noted that since FIG. 1 is a developed view, the oil pump 50 and an oil pan 37 are illustrated in the upper part of FIG. 1.

The oil pump 50 has a cylindrical sprocket supporting part 52 extending forward from a main body 51, for supporting a driven sprocket 55. The driven sprocket 55 is comprised of a disc 57 having teeth 56 formed at an outer peripheral edge thereof, and a boss 58 extending from the center of the disc 57 into the sprocket supporting part 52.

The boss 58 has a spline through-hole and is splined to a rotary shaft 53 of the oil pump 50. A bearing 59 is provided between the inner peripheral surface of the sprocket supporting part 52 and the boss 58, so that the driven sprocket 55 is supported by the sprocket supporting part 52 to rotate integrally with the rotary shaft 53 of the oil pump 50.

The disc 57 of the driven sprocket 55 is constructed such that the central part thereof in the vicinity of the boss 58 and the outer peripheral edge formed with the teeth 56 are offset from each other, and the teeth 56 and the bearing 59 overlap in the axial direction.

In the state in which the oil pump 50 is fixed on the oil pump mounting surface 33 of the transmission case 12, the teeth 56 of the driven sprocket 55 of the oil pump 50 and teeth 48 of the drive sprocket 47 supported by the hollow shaft 20 are aligned in the axial direction. A chain 60 is looped over the drive sprocket 47 and the driven sprocket 55, so that revolutions of the drive sprocket 47 are transmitted to the driven sprocket 55 to drive the oil pump 50.

As shown in a sectional view of FIG. 3, a chain guide 43 is projected by buildup welding from an end face on an outer peripheral edge of the housing cover 40, that is, an end face 42 facing the converter housing 11.As shown in FIG. 2, the driven sprocket 55 of the oil pump 50 is provided on the lower left side of the drive sprocket 47 on the main shaft 13, and the chain 60 is slacked (60R) in the lower right-hand part of FIG. 2.

Specifically, the chain guide 43 is provided on the housing cover 40 and in the vicinity of the driven sprocket 55, and comes into sliding contact with the slacked chain 60R to force the slacked side 60R of the chain 60 to move through a path closer to a tensioned side 60T of the chain 60. As a result, vibration of the slacked side 60R of the chain 60 can be suppressed in a path plane formed by two paths of a tensioned side 60T and the slacked side 60R of the chain 60, that is, inside the plane of FIG. 2.

According to the present embodiment arranged as described above, the chain guide 43 is provided to guide the slacked side 60R of the chain 60 through the path that can reduce the amount of the slack, vibration of the chain 60 can be suppressed to improve quietness, and poor engagement of the chain 60 and the driven sprocket 55 can be prevented, even if the accuracy of the center distance between the drive sprocket 47 and the driven sprocket 55 is not improved.

In particular, the chain guide 43 can be realized by an extremely simple structure because it is provided on the transmission case 12 side of the slacked side 60R of the chain 60 and in the vicinity of the slacked side 60R of the chain 60, i.e. the chain guide 43 is projected integrally from the housing cover 40 attached to the opening of the switching unit housing 30 in the transmission case 12.

Further, since the chain guide 43 is provided in the vicinity of the driven sprocket 55, the slacked side 60R of the chain 60 can be reliably engaged with the driven sprocket 55 in particular.

Further, since the chain guide 43 guides the slacked side 60R of the chain 60 through the path closer to the tensioned side 60T of the chain 60, the angle of engagement of the chain 60 and the driven sprocket 55 (the length of engagement) is increased to reduce load on the area of engagement of the chain 60 and the driven sprocket 55, thus increasing durability of the chain 60. 

1. An oil pump driving structure of an automatic transmission, comprising: an oil pump disposed apart from a main shaft of the automatic transmission; a chain looped over a drive sprocket provided on the main shaft and a driven sprocket of said oil pump, for transmitting revolutions from the drive sprocket to the driven sprocket; and a chain guide that guides a slacked side of said chain through a path that reduces an amount of slack thereof.
 2. An oil pump driving structure of an automatic transmission according to claim 1, wherein said chain guide is provided on a transmission case side of the slacked side of said chain and in vicinity of the slacked side of said chain.
 3. An oil pump driving structure of an automatic transmission according to claim 2, further including: a transmission case for the automatic transmission comprises a switching unit housing that houses a forward/backward switching unit, and a housing cover attached to an opening of the switching unit housing, wherein said chain guide is projected integrally from the housing cover.
 4. An oil pump driving structure of an automatic transmission according to claim 1, wherein said chain guide is provided in vicinity of the driven sprocket.
 5. An oil pump driving structure of an automatic transmission according to claim 1, wherein said chain guide guides the slacked side of said chain through a path closer to a tensioned side of said chain. 